Effect of altered SlSUT4 expression on the soluble sugar concentrations in the shoot apex and sucrose efflux. A to C) Concentrations of soluble sugars in shoot apex. D) Sucrose content of phloem exudates from detached, fully expanded tomato leaves. Exudation into 20 mM EDTA (pH 7.8) was allowed for 5 h in the dark. Data are means ± Sd (n = 3 to 5 for shoot apex sugar concentration and 12 for sucrose export rate). The data were subjected to Student's t-test, and asterisks above bars indicate significant differences compared with the wild type. *P < 0.05, **P < 0.01, and ***P < 0.001. FW, fresh weight; WT, wild type; O, overexpression line; R, RNAi line.